diff --git a/src/api/tcpip.c b/src/api/tcpip.c
index 3b635600..1b4f1504 100644
--- a/src/api/tcpip.c
+++ b/src/api/tcpip.c
@@ -140,7 +140,7 @@ ethernet_input(struct pbuf *p, struct netif *netif)
       etharp_ip_input( netif, p);
       #endif
       /* skip Ethernet header */
-      if(pbuf_header(p, (s16_t)(-sizeof(struct eth_hdr)))) {
+      if(pbuf_header(p, -(s16_t)sizeof(struct eth_hdr))) {
         LWIP_ASSERT("Can't move over header in packet", 0);
         pbuf_free(p);
         p = NULL;